In packaging of containers having closures thereon, it has been common to provide tamper indicating packages wherein the tamper indicating band is connected to the closure along the weakened line provided by a plurality of bridges and interengaging means between the band and the container are such that when the closure is unthreaded from the container, the band is severed along the bridge portions to indicate that the closure has been tampered with.
It has thus been recognized that a major problem with respect to such tamper indicating packages is that the bridges must be strong enough to withstand the forces of applying the closure to the container and yet be weak enough so that they do not require excessive force by the user in removing the closure from the container.
In one type of closure, the interengaging means between the band and the container comprises an annular bead on the inner surface of the band and a retaining bead on the finish of the container. Typical constructions of this type are shown in U.S. Pat. Nos. 3,329,295, 3,455,478, 3,784,041, 4,343,408, 4,352,436 and 4,461,390.
One of the major problems with respect to closures that use a continuous annular bead is that when the closure is applied to the container, a relatively high application torque is transmitted to the frangible bridges resulting in premature breakage. Generally attempts to resolve this problem include increasing the strength of the bridges. This creates a new problem during removal because the frangible bridges are then too strong and will not readily break. To resolve this problem, interference between the annular bead on the band and the retaining bead on the container can be changed but this leads back to the first problem, namely, that the frangible bridges will break during application. As a result, it is necessary in this type of closure to carefully control the tolerances of the internal diameter of the bead of the band and the outer diameter of the bead on the container. However, in the case of a glass container, such close tolerances cannot be readily maintained in accordance with normal glass manufacturing techniques and costly manufacture is required.
It has heretofore been suggested that projections be provided at circumferentially spaced points between the bridges to limit the degree of compression of the bridges during application of the closure to the container. Typical patents showing such an arrangement are U.S. Pat. Nos. 3,463,341, 4,352,436 and 4,461,390. However, this has not eliminated the problem since it is still very difficult to control the tolerances when the closure is being used particularly in connection with glass containers.
Other suggestions are shown, for example, in U.S. Pat. No. 3,455,478 which shows a tamper indicating closure wherein the bridges are inclined at an acute angle and extend rearwardly in a direction opposite to which the closure is rotated in order to place the bridges under compression and provide a greater resistance to rupture. The bridges are attached to the skirt and band and the bridges form acute angles with a recess in the skirt. As a result, one portion of the bridge is under compression while the other is under tension resulting in premature breakage.
In U.S. Pat. No. 3,463,341, the bridges are tapered toward the peripheral skirt and, in one form, inclined forwardly in the direction in which the closure is rotated As a result they are susceptible to premature breakage during application of the closure.
In U.S. Pat. No. 3,944,102, the bridges extend from abutments on the skirt and band so that the amount of compression during application of the closure is limited. The bridges stretch by vertical stretching during removal of the closure. The problem with such an arrangement is that the bridges do not provide any resistance against crushing during either the demolding or capping operation.
In U.S. Pat. No. 4,352,436, in addition to abutments or projections extending from the skirt of the closure toward the band, the bridges are inclined forwardly or in the direction in which the closure is rotated to remove the closure. It is contemplated that by this arrangement when the closure is applied, the bridges are stressed to limit the relative rotation of the closure and the band.
U.S. Pat. No. 4,461,391 shows projections on the skirt and band which have ratchet teeth which interengage to resist movement of the band when the closure is unscrewed.
U.S. Pat. No. 4,529,096 shows bridges that are inclined rearwardly with respect to the direction of rotation of the closure during removal from the container and, in addition, projections on the skirt which extend into recesses on the band to limit relative movement of the closure and band during application.
The aforementioned patents are directed to a premature breakage of frangible bridges during the capping operation and set forth features which are necessary when the tamper indicating structure relies on stretching of a solid annular bead of the tamper indicting band or ring over a retaining bead located on the container finish. As indicated earlier such arrangements require a relatively high application torque which is partially transmitted to the frangible bridges resulting in premature breakage. Attempts to resolve this problem by increasing the strength of these bridges creates a new problem during removal of the closure where the frangible bridges are then too strong and do not break. To resolve this problem, the interference between the tamper indicating band and the finish bead can be increased but this leads back to the initial problem namely frangible breakage during application. As a result, it is necessary in utilizing such constructions that the internal diameter of the tamper indicating band bead and the outer diameter of the finish bead must be controlled within close tolerances. This is extremely difficult particularly where the container is made of glass and the closure of plastic and such tolerances cannot readily be obtained at normal production speeds.
Where the tamper indicating band utilizes the flexing of a thin membrane of plastic about a hinge as, for example, in U.S. Pat. No. 4,550,844 and U.S. application Ser. No. 623,659 filed June 22, 1984, having a common assignee with the present application, the torque required to drive these wings or flexible band over the finished retaining bead is very low and as a result, there is no need for additional features to prevent premature bridge breakage during the capping operation.
Among the objectives of the present invention are to provide a tamper indicating package and closure preferably of the type shown in U.S. Pat. No. 4,550,840 and U.S. application Ser. No. 623,659 wherein frangible bridge construction is improved, permitting a larger axial opening or window between the bottom of the peripheral skirt of the closure and the top of the tamper indicating band so that the tamper indicating feature can be more readily viewed and ascertained; wherein the length of the frangible bridge is minimized; wherein the stretching of the frangible bridge is minimized; which forces the rupture or breakage of the frangible bridge at the base or free edge of the skirt of the closure providing a neat and more aesthetic appearance; which supports and protects the frangible bridges during demolding; which frangible bridge construction includes a stress concentrator at one corner of attachment to the bridge which will readily break upon removal of the closure or tampering with the closure.
In accordance with the invention, a tamper indicating package including a container having a neck with an external thread and an annular retaining bead below the thread and a plastic closure comprising a base wall, a peripheral skirt and a tamper indicating band connected to the free edge of the peripheral skirt by integral bridges. The tamper indicating band includes integral portions that extend below the annular bead on the container such that when the closure is unthreaded, the bridges are broken. The band includes circumferentially spaced supports that extend axially toward the free edge of the peripheral skirt and the bridges extend from the supports to the free edge. Each bridge includes a generally axial leading edge and a generally axial trailing edge. The upper edge of leading edge in the direction of unthreading intersects the lower edge of the skirt at a sharp corner to define a stress concentration point at the edge of the skirt. The lower edge of the leading edge of each bridge intersects and the band along a radius. The trailing edge intersects and the lower edge of the skirt and the upper edge of the band along radii. As a result when the closure is rotated to unthread it from the container, the bridges break at the stress concentration points at the edge of the skirt of the closure.